Cryogenic systems are finding an increasing number of applications in the low temperature storage or preservation of materials; for instance, biological elements or specimens, such as, animal or human embryos, tissues and blood cells; also, the freezing point determination of products for jet fuel or semi-conductors. The method and apparatus of the present invention is directed specifically to the controlled reduction of temperature, or cooling rate, in order to place those materials in a frozen state at extremely low temperatures. In the past, it has been found to be very critical to regulate the rate of cooling or reduction in temperature of many articles, particularly embryos, tissue, blood cells and the like both in order to reduce uneven temperatures within the chamber as well as to avoid any adverse effects on the materials to be preserved or frozen. Liquid nitrogen has been in wide use in the cooling and storage of articles in a cryogenic state because of its ability to drop the temperature to extremely low levels on the order of -35.degree. C. and less. The major problem in the use of liquid nitrogen for cryogenic devices is its lack of control over chamber temperature and its cooling rate as well as the cost of purchasing and storage of liquid nitrogen. It is therefore desirable to provide a method and means of reducing the temperature of articles which will permit the use of other gaseous mediums, such as, air which can be more closely controlled than liquid nitrogen in regulating the cooling rate of the articles and at the same time obviate the use of sophisticated controls and mediums, such as, liquid nitrogen, particularly in those temperature ranges found to be most critical in avoiding any damage or permanent alteration in the molecular structure of the articles being treated.
I am not aware of the utilization of air in the controlled cooling of articles under extremely low temperature conditions, such as, in the range of 0.degree. C. to -35.degree. C. Other apparatus has been devised which employs heat exchangers as well as temperature controllers in connection with monitoring apparatus for cell growth, depectinization of juices and fermentation systems. Representative patents in this area are U.S. Pat. Nos. 3,407,120 to R. E. Weiss et al.; 3,717,552 to J. C. Hondermarck et al.; 3,795,521 to J-P Richard; 4,036,699 to D. J. Quigg; 4,073,696 to H. Muller; and 4,238,337 to M. F. Peters et al. Nevertheless, none is directed to a cryogenic system for reducing the temperature of articles and materials, such as, encapsulated embryos, tissues or blood cells with the use of air as a gaseous medium in or through a temperature range of 0.degree. C. to -50.degree. C. in the manner in which I have devised.